Method and apparatus for preventing electrostatic fields in large tanks

ABSTRACT

In mammoth oil tanker cleaning operations, a procedure and apparatus to control and prevent formation of electrostatic charges in a tank. There is an electrostatic voltmeter to measure the field near the nozzle of a cleaning jet. The jet fluid is made up of a mixture of clean sea water with oily water, and the relative amount of each fluid in the mixture is controlled so as to produce a spray that has a neutral charge.

United States atet 1 1111 3,73@,i% Armistead I 51 Ma 1, i973 [5 METHOD AND APPARATUS FOR 3,121,027 2/1964 Galanor ..134/10 PREVENTING ELECTROSTATIC 3,164,747 1/1965 Yahnke 1,806,740 5/1931 Butterworth ..l34/24 [75] Inventor: Fontaine 'C. Armistead, Darien, OTHER CATIONS Conn v Klinkenberg et al., Electrostatics in the Petroleum In [73] Assignee: Texaco Development Corporation, dustl'yv (1958), PP- 27,

New York, NY. Primary Examiner-Joseph Scovronek [22] filed: 12, 1971 Assistant Examiner-D. G. Millman 21 Appl' 133 0 4 Attorney-Thomas H. Whaley and Carl 6. Ries [57] ABSTRACT [52] US. Cl ..l34/l0, 134/22 R, 134/24,

134/36, 134/57 R, 134/166 R, 317/2 R In mammoth oil tanker cleaning operations, a 51 1111.01 ..B08b 3/02 8081') 9/08 Pwcedure and apparatus and [58] Field of l 134/16 22 R 24 mation of electrostatic charges in a tank. There is an 134/36 109 1 electrostatic voltmeter to measure the field near the 166 i 236/3 317/2 nozzle of a cleaning jet. The jet fluid is made up of a mixture of clean sea water with oily water, and the relative amount of each fluid in the mixture is con- [56] References Cned trolled so as to produce a spray that has a neutral UNITED STATES PATENTS Charg 2,065,462 12/1936 Olsson ..134/22 R 13 Claims, 1 Drawing Figure CENTRIFUGAL SEPARATOR 2 Patented May 1, 1973 7 3,730,193

CENTRIFUGAL SEPARATOR METHOD AND APPARATUS FOR PREVENTING ELECTROSTATIC FWLDS IN LARGETANKS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the cleaning of large tanks, in general. More specifically, it concerns a particularly dangerous and difficult problem which has developed with the advent of modern mammoth tankers. In such large-sized tank ships, explosions have occurred with consequent heavy damage. These explosions have been related to the cleaning operations which involve use of a high-velocity fluid jet in washing down the walls of the tank. In order to carry different cargos, the tanks need to be washed following discharge of one cargo and before filling with the next.

2. Description of the Prior Art There have been different solutions suggested to take care of the problem, i.e., that relating to the cleaning of mammoth tanks. However, the proposed solutions had practical difficulties and, consequently, have not generally been put into use. Thus, it is an object of this inventionto provide a novel and effective solution to the problem, so as to prevent the build-up of dangerous electrostatic fields.

SUMMARY OF THE INVENTION Briefly, this invention concerns a method for preventing electrostatic fields in mammoth tank cleaning operations employing a high-velocity fluid jet. The method comprises the steps of taking a positive-chargeforming fluid and a negative-charge-forming fluid and mixing said fluids together to form a jet that has a neutral-charge-forming effect.

Again briefly, this invention relates to cleaning operations for mammoth tank ships, wherein a highvelocity jet is employed to wash down the walls of the tank, and the washing fluid is collected-in the sump. This method comprises the steps of withdrawing said washing fluid from the sump, and separating said washing fluid into heavier and lighter components. It also comprises the step of remixing said components and controlling the relative amounts of each in said jet in order to produce an electrically neutral atmosphere in said tank.

Once more, briefly, the invention relates to mammoth-tanker tank-cleaning and concerns a system for preventing electrostatic charge build-up. The system comprises in combination a jet nozzle for forming a high-velocity fluid jet to be directed toward the walls of said tank, and a swivel attached to said nozzle to effect rotation thereof with motor means for causing said rotation. It also comprises a pump for forcing a cleaning fluid through said nozzle. The said cleaning fluid comprises two components. One of said components is clean sea water which tends to produce a negative electrostatic charge. The other of said components is a mixture of oil and sea water which tends to produce a positive electrostatic charge. The system also comprises a mixing valve in series with said pump, and a sump for collecting run-off fluid from said tank walls. It also comprises a pair of containers to act as reservoirs for said components, and a centrifugal separator having an inlet and a pair of outlets. In addition, it comprises means for connecting said inlet to said sump, and means for connecting said outlets to said pair of containers, as well as conduit means for connecting said separated components to said mixing valve. It also comprises an electrostatic voltmeter associated with said jet nozzle, said voltmeter having an electrode for receiving the electrostatic potential in said tank. In addition, it comprises an electrode support member connected to said voltmeter and extending a predetermined distance beyond the discharge end of said nozzle, and control means for actuating said mixing valve in response to said electrostatic potential in a direction to reduce said potential toward zero.

BRIEF DESCRIPTION OF THE DRAWING The foregoing and other objects and benefits of the invention will be more fully set forth below in connection with the best mode contemplated by the inventor of carrying out the invention, and in connection with which there are illustrations provided in the drawing, wherein:

The FIGURE of drawings is a schematic illustrations of a system for carrying out the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention concerns a method. and/or apparatus that may be employed to prevent electrostatic fields in tank-cleaning (or in similar operations) wherever a fluid jet is used and, particularly, where such jet has a high velocity. It relates to the properties of the jet fluid and it'stems from a discovery that there will be a negative field produced by a jet of clean sea water. Concomitantly. it has been discovered that a jet of' fresh water, or sea water containing oil, or sea water containing a cleaning detergent, all will tend to produce a positive field.

Consequently, the method of this invention involves the following steps: (1) taking a positive-charge-forming fluid and a negative-charge-forming fluid. These may be, as indicated above, clean sea water for the former and oily sea water for the latter. (2) Mixing the foregoing fluids together to form a jet that produces a neutral charge. This step is carried out by maintaining the properties of the jet fluid in between those of the first fluid which would produce a positive field, and the second fluid which would produce a negative field; It will be appreciated that various ways'of maintaining this mixture could be employed. For example, the relative amount of oil in the mixture might be periodically determined and compared with a mixture that had been found by experiment to producea neutral field. Then appropriate adjustment could be made.

A system for carrying out the invention might take various forms, and a preferred embodiment is that illustrated in the FIGURE of drawings which illustrates schematically the elements'that are particularly applicable to use of the invention in modern mammoth tank ships. Thus, referring to the drawing, there is a sump 11 that collects the run-off fluids from a tankcleaning operation. Such fluid will, of course, be oily sea water 12 that collects in the sump 11. The tankcleaning process involves the use of a high-pressure fluid jet, e.g. a jet stream 15, that eminates from a jet nozzle 16 which is supported from a swivel 17. There is a motor 18'which may be employed for moving the nozzle 16 in rotation via the swivel 17.

The wash fluid that goes to make up the jet stream 15, is pumped through the swivel 17 to the nozzle 16 via any feasible piping. For example, there is a pipe 21 between the swivel 1'7 and nozzle l6, and another pipe 22 which connects the swivel 117 with a pump 23.

The pump 23 draws its intake fluid through a mixing valve 26 via another pipe 27. The components that go. to make up the fluid of the jet are controlled as to .relative amounts thereof by actuation of the mixing valve 26.

There is an actuator 30 which may take various forms, but which is scehmatically illustrated as being a diaphragm-type unit. Controls for actuator 30 are derived from an electrostatic voltmeter 31 that is attached to the nozzle 16 in any feasible manner such as is schematically indicated, i.e., by arm 32. Extending from the voltmeter 31, there is an insulated electrical conductor 35, which has an electrode 36 supported at the free end thereof. it will be appreciated that the electrode 36 is preferably spherical and is constructed of an electrically conductive material that will resist corrosion by the atmosphere encountered near the jet stream. In this manner, the electrode 36 will take on the same electrical charge as its surroundings.

Whenever there is a positive or negative charge registered by the voltmeter 311, it will be employed to actuate a control mechanism which may take various forms. The control system forms no part, per se, of the invention and it has been only schematically indicated by a dashed line 39. It will be understood by anyone skilled in the art that there are numerous socalled servo systems that would be applicable for use as the control link 39. In this manner, a control is applied to the actuator 30 so as to change the position of the mixing valve 26 in a proper direction for reducing the electrostatic charge that has been measured by the voltmeter 31 In accordance with the above-mentioned discovery,-

the jet stream 15 when made up of clean sea water, will produce a positive electrostatic field while, if the same stream 15 is oily sea water (such as would be expected in the sump 11 as a result of a washing operation) it would produce a negative electrostatic field. Consequently, in order to obtain relatively clean sea water separately from an oily mixture, there is a centrifugal separator 42 provided. Separator 42 .is supplied with fluid from the oily sea water 12 that is in the sump 11. This is indicated by a line 43 with arrow which connects the oily sea water 12 to the separator 42.

The separator 42 has two outlets which are schematically indicated by lines 46 and 47 which have arrows thereon. These transmit the separated fluids to a pair of containers 50 and 51, respectively. These containers will then act as reservoirs for the lighter and heavier components, respectively, of the fluid which has been separated. In this manner, a relatively fresh sea water component 54 will collect in the container 51, while a light oily component 55 will collect in the container 50.

The containers 50 and 51 have overflow outlets 56 and 57, respectively. These are merely provided in order to return any overflow back into the sump 11. Also, it may be noted that there is an inlet pipe 61 which has a valve 62 therein. This is connected to the container 51, and it permits the addition of clean sea water make-up in case it is needed.

The component fluids 54 and 55 are drawn through the mixing valve 26 by the pump 23, via a pair of pipes 65 and 66, respectively. These pipes connect the reservoirs to the mixing valve inlets so that proportional amounts of the components may be adjusted.

It will be appreciated from the foregoing that the system will act to prevent electrostatic charge build-up by having a continuous control for adjusting the mixing valve 26 whenever a positive or negative charge develops at electrode 36. Such adjustment will be in the direction that causes change in the constituency of the jet stream 15 so as to reduce the charge toward neutral or zero potential.

It will be appreciated that there could be other arrangements according to this invention and, particularly, with regard to the method, other and different types of apparatus might be employed in carrying out the difierent steps.

While the invention has been described above in considerable detail in accordance with the applicable statutes, this is not to be taken as in any way limiting the invention, but merely as being descriptive thereof.

WHAT I CLAIM IS:

1. A method for preventing electrostatic fields in mammoth tank cleaning operations employing a highvelocityfluid jet, comprising the steps of taking a positive-charge-forming fluid and a negative-charge-forming fluid; and

mixing said fluids together to form a jet having a neutral -charge-forming effect.

2. A method according to Claim 1, wherein said negative-charge-forming fluid is clean salt water.

3. A method according to Claim 2, wherein said positive-charge-forming fluid is a mixture of water with oil.

4. A method according to Claim 3, further comprising the steps of measuring the electrostatic field created by said jet;

and

controlling said mixture in order to maintain a neutral electrostatic field.

5. In cleaning operations for mammoth tank ships, wherein a high-velocity jet is employed to wash down the walls of a tank and the washing fluid is collected in a sump, the method comprising withdrawing said washing fluid from the sump;

separating said washing fluid into heavier and lighter components; and

remixing said components and controlling the relative amounts of each in said jet in order to produce an electrically neutral atmosphere in said tank.

6. In cleaning operations according to Claim 5, the method further comprising measuring the electrostatic charge of said atmosphere; and

controlling said relative amounts in accordance with said measurement.

7. In mammoth tanker tank-cleaning, a system for preventing electrostatic charge build-up, comprising in combination jet nozzle means for forming a high-velocity fluid jet to be directed against the walls of said tank;

pump means for forcing a cleaning fluid through said nozzle;

said cleaning fluid having at least two components;

one of said components tending to form a negative electrostatic field and the other tending to form a positive electrostatic field; and means for regulating the relative percentages of said two components in order to maintain a neutral electrostatic field in said tank; said last named means comprising a mixing valve; means for determining the electrostatic field potential in said tank; and means for actuating said mixing valve in response to said electrostatic potential so as to reduce said potential toward zero. 8. A system according to Claim 7, further comprising a sump for collecting run-off fluid from said cleaning; means for separating said run-off fluid into said two components; and means for supplying said separated components to said mixing valve. 9. A system according to Claim 8, wherein said separating means is centrifugal; and said supplying means comprises a container for each of separated components; and conduit means for connecting said mixing valve with said containers. 10. A system according to Claim 7, wherein said electrostatic field determining means comprises an electrostatic voltmeter; means for supporting said voltmeter from said nozzle; an electrode for receiving the static potential in said tank; and electrode support means for holding said electrode an extended distance beyond the discharge end of said nozzle. 1 l. A system according to Claim 10, further comprising a sump for collecting run-off fluid from said cleaining; means for separating said run-off fluid into said two components; and means for supplying said separated components to said mixing valve. -12. A system according to Claim 11, wherein said separating means is centrifugah'and said supplying means comprises a container for each of said separated components;

and

conduit means for connecting said mixing valve with said containers.

13. In mammoth tanker tank-cleaning, a system for preventing electrostatic charge build-up, comprising in combination a jet nozzle for forming a high-velocity fluid jet to be directed against the walls of said tank;

a swivel attached to said nozzle to permit rotation thereof, with motor means for causing said rotation;

a pump for forcing a cleaning fluid through said nozzle;

said cleaning fluid being comprised of two components;

one of said components being clean sea water which tends to produce a negative electrostatic charge; the other of said components being a mixture of oil and sea water which tends to produce a positive electrostaticcharge;

a mixing valve in series with said pump;

a sump for collecting run-off fluid from said tank walls;

a pair of containers to act as reservoirs for said coma centrifugal separator having an inlet and a pair of outlets;

means for connecting said inlet to said pump;

means for connecting said outlets to said pair of containers;

conduit means for connecting said separated components to said mixing valve;

an electrostatic voltmeter associated with said jet nozzle;

said voltmeter having an electrode for receiving the electrostatic potential in said tank;

an electrode support member connected to said voltmeter and extending a predetermined distance beyond the discharge end of said nozzle; and

control means for actuating said mixing valve in response to said electrostatic potential in a direction to reduce said potential toward zero. 

1. A method for preventing electrostatic fields in mammoth tank cleaning operations employing a high-velocity fluid jet, comprising the steps of taking a positive-charge-forming fluid and a negative-chargeforming fluid; and mixing said fluids together to form a jet having a neutralcharge-forming effect.
 2. A method according to Claim 1, wherein said negative-charge-forming fluid is clean salt water.
 3. A method according to Claim 2, wherein said positive-charge-forming fluid is a mixture of water with oil.
 4. A method according to Claim 3, further comprising the steps of measuring the electrostatic field created by said jet; and controlling said mixture in order to maintain a neutral electrostatic field.
 5. In cleaning operations for mammoth tank ships, wherein a high-velocity jet is employed to wash down the walls of a tank and the washing fluid is collected in a sump, the method comprising withdrawing said washing fluid from the sump; separating said washing fluid into heavier and lighter components; and remixing said components and controlling the relative amounts of each in said jet in order to produce an electrically neutral atmosphere in said tank.
 6. In cleaning operations according to Claim 5, the method further comprising measuring the electrostatic charge of said atmosphere; and controlling said relative amounts in accordance with said measurement.
 7. In mammoth tanker tank-cleaning, a system for preventing electrostatic charge build-up, comprising in combination jet nozzle means for forming a high-velocity fluid jet to be directed against the walls of said tank; pump means for forcing a cleaning fluid through said nozzle; said cleaning fluid having at least two components; one of said components tending to form a negative electrostatic field and the other tending to form a positive electrostatic field; and means for regulating the relative percentages of said two components in order to maintain a neutral electrostatic field in said tank; said last named means comprising a mixing valve; means for determining the electrostatic field potential in said tank; and means for actuating said mixing valve in response to said electrostatic potential so as to reduce said potential toward zero.
 8. A system according to Claim 7, further comprising a sump for collecting run-off fluid from said cleaning; means for separating said run-off fluid into said two components; and means for supplying said separated components to said mixing valve.
 9. A system according to Claim 8, wherein said separating means is centrifugal; and said supplying means comprises a container for each of separated components; and conduit means for connecting said mixing valve with said containers.
 10. A system according to Claim 7, wherein said electrostatic field determining means comprises an electrostatic voltmeter; means for supporting said voltmeter from said nozzle; an electrode for receiving the static potential in said tank; and electrode support means for holding said electrode an extended distance beyond the discharge end of said nozzle.
 11. A system according to Claim 10, further comprising a sump for collecting run-off fluid from said cleaining; means for separating said run-off fluid into said two components; and means for supplying said separated components to said mixing valve.
 12. A system according to Claim 11, wherein said separating means is centrifugal; and said supplying means comprises a container for each of said separated components; and conduit means for connecting said mixing valve with said containers.
 13. In mammoth tanker tank-cleaning, a system for preVenting electrostatic charge build-up, comprising in combination a jet nozzle for forming a high-velocity fluid jet to be directed against the walls of said tank; a swivel attached to said nozzle to permit rotation thereof, with motor means for causing said rotation; a pump for forcing a cleaning fluid through said nozzle; said cleaning fluid being comprised of two components; one of said components being clean sea water which tends to produce a negative electrostatic charge; the other of said components being a mixture of oil and sea water which tends to produce a positive electrostatic charge; a mixing valve in series with said pump; a sump for collecting run-off fluid from said tank walls; a pair of containers to act as reservoirs for said components; a centrifugal separator having an inlet and a pair of outlets; means for connecting said inlet to said pump; means for connecting said outlets to said pair of containers; conduit means for connecting said separated components to said mixing valve; an electrostatic voltmeter associated with said jet nozzle; said voltmeter having an electrode for receiving the electrostatic potential in said tank; an electrode support member connected to said voltmeter and extending a predetermined distance beyond the discharge end of said nozzle; and control means for actuating said mixing valve in response to said electrostatic potential in a direction to reduce said potential toward zero. 